Reciprocating compressor

ABSTRACT

According to the present invention, a recess ( 25 ) which is induction means is provided in a top end surface ( 24 ) of a piston ( 16 ), the recess ( 25 ) guides working fluid ( 3 ) staying near an inner peripheral surface of a compression chamber ( 13 ) from an outer peripheral edge of the top end surface ( 24 ) toward an opposite position of the top end surface ( 24 ) facing a discharge hole ( 19 ), and the recess ( 25 ) smoothens discharging motion of working fluid ( 3 ) from the discharge hole ( 19 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reciprocating compressor used for an air compressor and a refrigeration cycle apparatus such as a refrigerator.

2. Description of the Related Art

In recent years, to protect global environment, demands for energy saving of various devices are increasingly strengthened, and it is strongly desired to enhance efficiencies of a compressor used for a refrigerator or other refrigeration cycle apparatus, and a reciprocating compressor such as an air compressor used in an industrial field.

As a conventional reciprocating compressor of this kind, there is known a compressor in which a recess is formed in an upper surface of a piston movable in reciprocating motion in a cylinder to enhance the efficiency of the compressor as disclosed in Examined Japanese Patent Application, Publication No. H08-6689.

FIG. 19 is a sectional view of the conventional reciprocating compressor described in the patent document, FIG. 20 is a plan view of a piston of the conventional reciprocating compressor as viewed from its top end surface, and FIG. 21 is an enlarged sectional view of an upper portion of the piston and a valve plate portion of the conventional reciprocating compressor.

As shown in FIGS. 19, 20 and 21, oil 102 is stored in a bottom in airtight container 101 of this reciprocating compressor, working fluid 103 is charged into airtight container 101, and compressor body 104 is accommodated in airtight container 101.

Compressor body 104 is resiliently supported in airtight container 101 by suspension spring 105.

Compressor body 104 includes electromotive element 106 and compressing element 109 rotated and driven by electromotive element 106. Compressing element 109 is disposed below electromotive element 106, and electromotive element 106 includes stator 107 and rotor 108.

Compressing element 109 includes crankshaft 112 having eccentric shaft 110 and main shaft 111. Compressing element 109 also includes block 115 in which cylinder 114 forming compression chamber 113 and bearing portion 123 supporting main shaft 111 are integrally formed. Compressing element 109 also includes piston 116 movable in reciprocating motion in cylinder 114.

Compressing element 109 includes a valve plate 117 which closes an end surface of cylinder 114, and suction valve 120 and discharge valve 121 which are provided in valve plate 117 for respectively opening and closing a suction hole (not shown) and discharge hole 119. Inside and outside of the compression chamber 113 are communication through the suction hole and discharge hole 119. Compressing element 109 also includes connecting means 122 which connects eccentric shaft 110 and piston 116 with each other.

Cylinder head 128 covering valve plate 117 is disposed on valve plate 117 on a side opposite from compression chamber 113, and head space 129 is formed by valve plate 117 and cylinder head 128.

Main shaft 111 of crankshaft 112 is rotatably supported by bearing portion 123 of block 115, and rotor 108 is fixed to main shaft 111.

As shown in FIGS. 20 and 21, recess 125 is formed in an upper surface (top end surface) 124 of piston 116, at least a portion of recess 125 is superposed on a portion of discharge hole 119, surface 126 of upper surface 124 other than recess 125 is flat, and is parallel to a surface of valve plate 117 on the side of compression chamber 113.

Next, operation of the conventional reciprocating compressor is described.

In the reciprocating compressor, current flows through stator 107 to generate a magnetic field, thereby rotating rotor 108 fixed to main shaft 111 to rotate crankshaft 112, so that piston 116 reciprocates in cylinder 114 through connecting means 122 mounted on eccentric shaft 110, and a series of cycle of suction stroke, compression stroke and discharge stroke is repeated.

In the suction stroke, if piston 116 moves in a direction increasing a capacity of cylinder 114, working fluid 103 in compression chamber 113 expands, and if a pressure in compression chamber 113 becomes smaller than a suction pressure, a pressure difference is generated between a pressure in compression chamber 113 and a pressure of a refrigeration cycle low-pressure side (not shown).

This pressure difference causes suction valve 120 to start opening, and low-temperature working fluid 103 which returns from the refrigeration cycle flows into compression chamber 113 through the suction hole (not shown).

In the compression stroke, if the operation of piston 116 is shifted from a position of the bottom dead center where the capacity of the compression chamber 113 becomes the greatest to a direction in which the capacity of compression chamber 113 is reduced, a pressure in the compression chamber 113 rises, suction valve 120 is closed by a difference between the pressure in the compression chamber 113 and the refrigeration cycle low-pressure side (not shown), and the compression chamber 113 is closed.

Thereafter, if the piston 116 is further operated in the direction where the capacity of the compression chamber 113 is reduced, working fluid 103 is compressed and the pressure rises to a predetermined value.

In the discharge stroke, a pressure of working fluid 103 in compression chamber 113 rises, and the pressure becomes higher than a pressure in head space 129 formed by valve plate 117 and cylinder head 128.

Then, the pressure difference causes discharge valve 121 to start opening, working fluid 103 in compression chamber 113 passes through discharge hole 119 and flows out into head space 129. Thereafter, working fluid 103 is discharged from head space 129 to a refrigeration cycle high-pressure side (not shown) through a discharge muffler (not shown).

When piston 116 most approaches valve plate 117 and reaches the top dead center where the capacity of the compression chamber 113 becomes the minimum, a clearance exists between piston 116 and valve plate 117 to avoid interference therebetween, and very small capacity 127 remains in compression chamber 113.

Hence, the working fluid remains in very small capacity 127 and the working fluid is not discharged out. Therefore, in the suction stroke, remaining working fluid 103 and new working fluid 103 which flows into compression chamber 113 through the suction hole (not shown) are mixed and compressed.

That is, increase in a capacity of very small capacity 127 means a deterioration of compression rate of working fluid 103, and this lowers the volumetric efficiency.

However, if a capacity of very small capacity 127 is excessively reduced to enhance the volumetric efficiency, a passing-sectional area through which working fluid 103 flows to discharge hole 119 becomes narrow, and there is a possibility that flow of working fluid 103 is hindered and the working fluid is excessively compressed. As a result, there is a possibility that input of the compressor is increased and the compressor efficiency is deteriorated.

Hence, according to the conventional reciprocating compressor, recess 125 is formed in upper surface 124 of piston 116. Therefore, when piston 116 reaches the top dead center, the clearance of very small capacity 127 between valve plate 117 and recess 125 is widened, and it is possible to widely ensure the passing-sectional area through which working fluid 103 flows from upper surface 124 of piston 116 to discharge hole 119 through very small capacity 127.

As a result, it is possible to improve the flow of working fluid 103 flowing to discharge hole 119, a clearance distance between valve plate 117 and upper surface 124 of piston 116 when piston 116 reaches the top dead center is narrowed, the very small capacity 127 is reduced and it is possible to improve the volumetric efficiency of the compressor.

According to the conventional structure, however, since working fluid 103 flows toward the central portion of recess 125 near recess 125 and upper surface 124 of piston 116 in the compression stroke in which piston 116 moves in a reducing direction of the capacity of compression chamber 113, two flows of working fluid 103 intersect at the central portion of recess 125.

As a result, the flow of working fluid 103 in compression chamber 113 when working fluid 103 is compressed is disturbed and thus, the flow of working fluid 103 flowing toward discharge hole 119 is hindered.

Therefore, the conventional structure has a problem that weight of working fluid 103 which remains in a space capacity between piston 116 and valve plate 117 when piston 116 reaches the top dead center increases, remaining working fluid 103 expands again during the suction stroke and the volumetric efficiency is lowered.

SUMMARY OF THE INVENTION

According to a reciprocating compressor of the present invention, induction means is provided on a top end surface of a piston located on the side of a compression chamber, the induction means guides working fluid staying near an inner peripheral surface of a compression chamber from an outer peripheral edge of the top end surface toward an opposite position of the top end surface facing the discharge hole.

At the time of a compression stroke in which the piston moves from the bottom dead center to the top dead center, a capacity of the compression chamber is reduced as the piston moves, working fluid in the compression chamber is compressed and is discharged from the discharge hole.

At this time, working fluid staying near the inner peripheral surface of the compression chamber (outer peripheral edge of the piston top end surface) flows to the opposite position of the top end surface of the piston facing the discharge hole along the induction means, and residence of the working fluid near the inner peripheral surface of the compression chamber is suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a vertical sectional view of a reciprocating compressor according to a first embodiment of the present invention;

FIG. 2 is an exploded perspective view of a compressing element of the reciprocating compressor according to the first embodiment of the invention;

FIG. 3 is a perspective view of a piston constituting the compressing element of the reciprocating compressor according to the first embodiment of the invention;

FIG. 4 is a plan view of the piston of the reciprocating compressor according to the first embodiment of the invention.

FIG. 5 is a vertical sectional view of the piston of the reciprocating compressor according to the first embodiment of the invention taken along the line 5-5 in FIG. 3;

FIG. 6 are schematic views for explaining operation of the reciprocating compressor according to the first embodiment of the invention;

FIG. 7 is a graph showing a comparison result between the reciprocating compressor of the first embodiment and a compressor having the conventional structure concerning refrigeration ability, input and coefficient of performance (COP);

FIG. 8 are schematic diagrams for explaining a flow of working fluid in a compression stroke of the reciprocating compressor according to the first embodiment of the invention;

FIG. 9 is a perspective view of a piston of a reciprocating compressor according to a second embodiment of the invention;

FIG. 10 is a plan view of the piston of the reciprocating compressor according to the second embodiment of the invention;

FIG. 11 is a vertical sectional view of the reciprocating compressor according to the second embodiment of the invention taken along the 11-11 line in FIG. 9;

FIG. 12 are schematic diagrams for diagram for explaining a flow of working fluid in a compression stroke of the reciprocating compressor according to the second embodiment of the invention;

FIG. 13 is a perspective view of a piston of a reciprocating compressor according to a third embodiment of the invention;

FIG. 14 is a plan view of the piston of the reciprocating compressor according to the third embodiment of the invention;

FIG. 15 is a vertical sectional view of the reciprocating compressor according to the third embodiment of the invention taken along the 15-15 line in FIG. 13;

FIG. 16 is a perspective view of a piston of a reciprocating compressor according to a fourth embodiment of the invention;

FIG. 17 is a plan view of the piston of the reciprocating compressor according to the fourth embodiment of the invention;

FIG. 18 is a vertical sectional view of the reciprocating compressor according to the fourth embodiment of the invention taken along the 18-18 line in FIG. 16;

FIG. 19 is a sectional view of a conventional reciprocating compressor;

FIG. 20 is a plan view of a piston of the conventional reciprocating compressor as viewed from a top end surface of the piston; and

FIG. 21 is an enlarged sectional view of an upper portion of the piston and a valve plate portion of the conventional reciprocating compressor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described with reference to the drawings. The invention is not limited to the embodiments.

First Embodiment

FIG. 1 is a vertical sectional view of a reciprocating compressor according to a first embodiment of the present invention. FIG. 2 is an exploded perspective view of a compressing element of the reciprocating compressor according to the first embodiment. FIG. 3 is a perspective view of a piston constituting the compressing element of the reciprocating compressor according to the first embodiment. FIG. 4 is a plan view of the piston of the reciprocating compressor according to the first embodiment. FIG. 5 is a vertical sectional view of the piston of the reciprocating compressor according to the first embodiment taken along the line 5-5 in FIG. 3.

In FIGS. 1 to 5, the reciprocating compressor has airtight container 1 in a bottom of which oil 2 is stored, and working fluid 3 such as a hydrocarbon-based refrigerant having a low global warming potential, e.g. R600a is charged.

Airtight container 1 includes suction pipe 50 and discharge pipe 57 formed by a drawing press die of an iron plate. One end of suction pipe 50 is in communication with airtight container 1 and the other end of suction pipe 50 is connected to a refrigeration cycle low-pressure side (not shown). One end of discharge pipe 57 passes through airtight container 1 and is in communication with a discharge muffler (not shown) and the other end of the discharge pipe 57 is connected to a refrigeration cycle high-pressure side (not shown).

Compressor body 4 including compressing element 9 and electromotive element 6 which drives compressing element 9 is accommodated in airtight container 1. Compressor body 4 is resiliently supported by suspension spring 5 with respect to airtight container 1.

Compressing element 9 includes, for example, crankshaft 12, cylinder block 15, piston 16 and connecting means 22. Crankshaft 12 includes eccentric shaft 10 and main shaft 11. Oil-feeding mechanism 51 including a spiral groove is formed on a surface of main shaft 11.

Electromotive element 6 includes stator 7 which is fixed to a lower portion of cylinder block 15 by means of a bolt (not shown), and rotor 8 disposed in stator 7 and fixed to main shaft 11 by shrink-fitting.

Cylinder 14 constituting compression chamber 13 and bearing portion 23 which rotatably support main shaft 11 are integrally formed on cylinder block 15.

Valve plate 17 having suction hole 18 and discharge hole 19 which bring inside and outside of compression chamber 13 into communication with each other, suction valve 20 which opens and closes suction hole 18, and cylinder head 52 which covers valve plate 17 are fixed to an end surface of cylinder 14 by head bolt 53 such as to seal the end surface of the cylinder 14.

Suction muffler 54 is grasped and fixed between valve plate 17 and cylinder head 52. Discharge valve 21 which opens and closes discharge hole 19 is fixed to a surface of valve plate 17 facing cylinder head 52, and head space 56 is formed by valve plate 17 and cylinder head 52.

As shown in FIG. 3, recess 25 of a predetermined width is provided in top end surface 24 of piston 16 facing valve plate 17, and recess 25 extends in a radial direction from outer peripheral edge 27 of piston 16 farthest from discharge hole 19 toward a position of top end surface 24 facing discharge hole 19. Recess 25 corresponds to induction means of the present invention, and the induction means has a uniform depth (e.g., about 50 μm).

Truncated conical projection 26 is provided at a position of top end surface 24 of piston 16 facing discharge hole 19. Since projection 26 is provided at the position facing discharge hole 19, its projecting (height) size is set such that projection 26 comes into and out from discharge hole 19 provided in valve plate 17 in a state where piston 16 reaches the top dead center.

Next, operation and effect of the reciprocating compressor having the above-described configuration are described.

In the reciprocating compressor, current flows through stator 7 to generate a magnetic field, thereby rotating rotor 8 fixed to main shaft 11, so that crankshaft 12 is rotated. With this, piston 16 reciprocates in cylinder 14 through connecting means 22 which is rotatably mounted on eccentric shaft 10.

With the reciprocating motion of piston 16, working fluid 3 is sucked into compression chamber 13 through suction muffler 54, and compressed. Thereafter, working fluid 3 is discharged from discharge hole 19, and flows into the refrigeration cycle (not shown) through head space 56.

Next, the suction stroke, the compression stroke and the discharge stroke of working fluid 3 carried out by compressor body 4 are described with reference to FIG. 6.

FIG. 6 are schematic diagrams for explaining operation of the reciprocating compressor according to the first embodiment of the invention, wherein FIG. 6A shows midst of the suction stroke, FIG. 6B shows completion (near the bottom dead center) of the suction stroke, FIG. 6C shows midst of the compression stroke, and FIG. 6D shows the discharge stroke (near the top dead center).

In the suction stroke, when piston 16 operates in a direction of an arrow x in which the capacity of compression chamber 13 increases as shown in FIG. 6A, working fluid 3 in compression chamber 13 expands and a pressure in compression chamber 13 decreases. When the pressure in compression chamber 13 becomes lower than that in suction muffler 54, suction valve 20 is opened by the pressure difference between the pressure in compression chamber 13 and the pressure in suction muffler 54. With this, low temperature working fluid 3 which returned from the refrigeration cycle is once released from suction pipe 50 into airtight container 1 and then, working fluid flows into compression chamber 13 through suction muffler 54.

Thereafter, in the compression stroke, when the operation of piston 16 is shifted from the bottom dead center into a direction of an arrow y in which the capacity of compression chamber 13 decreases as show in FIG. 6B, the pressure in compression chamber 13 rises, and suction valve 20 is closed by the pressure difference between the pressure in compression chamber 13 and the pressure in suction muffler 54. With this, compression chamber 13 is closed, piston 16 further operates in the direction in which the capacity of compression chamber 13 decreases and with this, working fluid 3 is compressed and a pressure thereof rises to a predetermined value as shown in FIG. 6C.

In the discharge stroke, when the pressure of working fluid 3 in the compression chamber 13 rises and becomes higher than a pressure in head space 56 formed by valve plate 17 and cylinder head 52, discharge valve 21 starts opening by the pressure difference as shown in FIG. 6D. As a result, working fluid 3 in compression chamber 13 flows out into head space 56 through discharge hole 19.

Working fluid 3 flows from head space 56 into a refrigeration cycle high-pressure side (not shown) through discharge pipe 57 via the discharge muffler (not shown).

When the pressure in compression chamber 13 becomes lower than that in head space 56, the discharge valve 21 closes and with this, compression chamber 13 closes, piston 16 moves toward the bottom dead center and the stroke is again shifted to the suction stroke.

In the position of the top dead center of piston 16, a clearance is formed between piston 16 and valve plate 17 for avoiding interference therebetween, and a very small capacity remains in compression chamber 13.

That is, due to this very small capacity, working fluid 3 remains in compression chamber 13. Since remaining working fluid 3 is not discharged, remaining working fluid 3 and another working fluid 3 which newly flows in from suction muffler 54 through suction hole 18 are mixed and compressed in the suction stroke.

Therefore, according to the conventional configuration, working fluid 3 which remains near the inner peripheral surface of compression chamber 13 again expands, and expected improvement of the compression efficiency is limited.

According to the configuration of the compressor of the first embodiment, however, since recess 25 is provided in top end surface 24 of piston 16 and recess 25 extends from outer peripheral edge 27 of piston 16 farthest from discharge hole 19 toward the position of top end surface 24 facing discharge hole 19 as shown in FIGS. 3 to 5, compressed working fluid 3 which exists near the inner peripheral surface of compression chamber 13 can be discharged from discharge hole 19 to the extent possible, and effect greater than that of the conventional technique can be expected.

FIG. 7 is a graph showing a comparison result between the reciprocating compressor of the first embodiment of the invention and a compressor having the conventional configuration concerning refrigeration ability, input and coefficient of performance (COP).

FIG. 7 shows a result of refrigeration ability, input (power consumption) and COP (coefficient of performance) of the compressor having the configuration of the first embodiment.

As shown in FIG. 7, under the same test condition, the input is higher than that of the conventional configuration, but since the refrigeration ability is much higher than that of the conventional configuration, the COP is higher than that of the conventional configuration.

A flow of working fluid 3 in compression chamber 13 during the compression stroke and the discharge stroke is described with reference to FIG. 8.

FIG. 8 are schematic diagrams showing the flow of working fluid in the compression stroke of the reciprocating compressor according to the first embodiment, wherein FIG. 8A shows a state immediately before the compressing operation is started (immediately before the suction operation is completed, near the bottom dead center), FIG. 8B shows midst of the compression stroke, and FIG. 8C shows the discharge stroke.

When piston 16 starts in a direction of an arrow y from the state immediately before the compressing operation is started as shown in FIG. 8A and a pressure in compression chamber 13 becomes higher than that in suction muffler 54, suction valve 20 closes.

As shown in FIG. 8B, compression chamber 13 is closed, piston 16 operates in a direction of the top dead center, i.e., a direction in which the capacity of compression chamber 13 decreases, and working fluid 3 is compressed.

At this time, working fluid 3 in compression chamber 13 flows from an inner peripheral surface of compression chamber 13 toward discharge hole 19 along a bottom surface of recess 25 as shown with the arrow Y by recess 25 formed in top end surface 24 of piston 16 near top end surface 24 of piston 16.

When the pressure in compression chamber 13 becomes higher than that in head space 56 and discharge valve 21 opens as shown in FIG. 8C, working fluid 3 near discharge hole 19 swiftly flows toward discharge hole 19 as shown with an arrow Y1, passes through discharge hole 19 and is discharged into head space 56.

Working fluid 3 in region Z (near the inner peripheral surface of compression chamber 13) which is separated away from discharge hole 19 and which is shown in FIG. 4 receives influence of a flow shown with the arrow Y1 as shown with an arrow Y2 in FIG. 8C, a portion of working fluid 3 flows toward the inner peripheral surface of compression chamber 13 and normally, it can be estimated that discharging operation of working fluid 3 from discharge hole 19 becomes slow.

However, according to the configuration of the first embodiment, since top end surface 24 of piston 16 is provided with recess 25, it can be estimated that a constant flow of working fluid 3 staying near the inner peripheral surface of compression chamber 13 is formed by recess 25 as shown with an arrow Y3 and working fluid 3 is guided toward projection 26.

As a result, piston 16 reaches a position near the top dead center and thus, the clearance between top end surface 24 and valve plate 17 becomes small, and even if a path leading to discharge hole 19 becomes narrow, it can be estimated that working fluid 3 remaining in region Z is induced by a flow (arrow Y3) of working fluid 3 flowing through recess 25 of top end surface 24 of piston 16, and working fluid 3 is smoothly discharged from discharge hole 19. Therefore, a weight of remaining working fluid 3 is reduced and an amount of re-expansion is suppressed and with this, it is possible to enhance the volumetric efficiency.

Further, as working fluid 3 produced by recess 25 formed in top end surface 24 of piston 16 flows, working fluid 3 in the region Z of piston 16 shown in FIG. 4 is smoothly discharged from discharge hole 19 to head space 56 without staying in region Z of piston 16.

Hence, it is possible to moderate a local pressure rise around outer peripheral edge 27 of top end surface 24 of piston 16 generated by the residence of working fluid 3, and to reduce excessive compression in which a pressure rises more than necessary. It is also possible to reduce the compressor input and to enhance the compressor efficiency.

Working fluid 3 staying near the inner peripheral surface of compression chamber 13 is induced by a flow of working fluid 3 flowing through recess 25 provided in top end surface 24 of piston 16, and working fluid 3 is discharged from discharge hole 19. Therefore, it is possible to further narrow the clearance between piston 16 and valve plate 17. Hence, the capacity of compression chamber 13 at the position of the top dead center of piston 16 can further be set small. With this, it is possible to expect that the weight of remaining working fluid 3 is further reduced, the amount of re-expansion is suppressed and the volumetric efficiency is further enhanced.

Since projection 26 which enters discharge hole 19 is formed on top end surface 24 of piston 16, projection 26 enters discharge hole 19 during the discharge stroke, and it is possible to reduce the capacity of compression chamber 13 also including the capacity of discharge hole 19 in the top dead center position. Moreover, the weight of the remaining working fluid is reduced so that the amount of re-expansion is reduced, and therefore, it is possible to further enhance the volumetric efficiency.

In the first embodiment, discharge hole 19 is provided at a location which is offset from a central portion of top end surface 24 with respect to top end surface 24 of piston 16. Hence, recess 25 provided in top end surface 24 of piston 16 is provided from outer peripheral edge 27 of piston 16 farthest from discharge hole 19 toward projection 26 which is in an opposite position of top end surface 24 of piston 16 facing discharge hole 19.

Also if discharge hole 19 reaches the central portion of top end surface 24 of piston 16, a similar effect can be expected by providing recess 25 such as to extend from outer peripheral edge 27 of piston 16 where working fluid 3 stays toward a position facing discharge hole 19.

Although projection 26 provided on piston 16 is formed into the truncated conical shape in the first embodiment, the shape of the projection 26 is not limited to the truncated conical shape, and even if projection 26 is formed into a truncated polygonal pyramid shape such as a truncated square pyramid shape, a similar effect can be expected.

Although top end surface 24 of piston 16 is provided with projection 26 in the first embodiment, even if top end surface 24 is not provided with projection 26, it is possible to induce working fluid 3 remaining in region Z of piston 16 shown in FIG. 4 and to guide working fluid 3 into discharge hole 19 by a forcible flow of working fluid 3 flowing through recess 25.

Therefore, also in the piston configuration in which top end surface 24 of piston 16 is not provided with projection 26, it is possible to expect the effect of reducing the weight of working fluid 3 remaining in compression chamber 13, suppressing the amount of re-expansion, and enhancing the volumetric efficiency.

Second Embodiment

FIG. 9 is a perspective view of a piston of a reciprocating compressor according to a second embodiment of the invention. FIG. 10 is a plan view of the piston of the reciprocating compressor according to the second embodiment of the invention. FIG. 11 is a sectional view of the reciprocating compressor according to the second embodiment of the invention taken along the 11-11 line in FIG. 9. FIG. 12 are schematic diagrams for diagram for explaining a flow of working fluid in a compression stroke of the reciprocating compressor according to the second embodiment of the invention, wherein FIG. 12A shows a state immediately before a compressing operation is started (immediately before a sucking operation is completed, near the bottom dead center), FIG. 12B shows midst of the compression stroke, and FIG. 12C shows the discharge stroke. The same or corresponding constituent elements as those in the first embodiment are designated with the same symbols and the second embodiment is described.

As shown in FIGS. 9, 10 and 11, in piston 16 of the reciprocating compressor according to the second embodiment of the invention, like the first embodiment, recess 25 a of a predetermined width extends from outer peripheral edge 27 of piston 16 farthest from discharge hole 19. The recess 25 a extends along a diametric direction of top end surface 24 and passes through an opposite position of top end surface 24 facing discharge hole 19. Recess 25 a corresponds to induction means of the invention, and its bottom surface is formed into inclined in a manner to increase a distance from valve plate 17 toward the opposite position of top end surface 24 facing discharge hole 19.

In other words, recess 25 a is formed such that its bottom becomes deeper toward the opposite position of top end surface 24 of piston 16 facing discharge hole 19, so that the height from the bottom to the top end surface 24 changes, for example, from 0 μm to 50 μm.

Truncated conical projection 26 is provided at the position of top end surface 24 of piston 16 facing discharge hole 19. Since projection 26 is provided at the position facing discharge hole 19, its projecting (height) size is set such that projection 26 enters discharge hole 19 provided in valve plate 17 in a state where piston 16 reaches the top dead center.

Piston 16 having the above-described configuration is used instead of piston 16 of the compressor described in the first embodiment, the same description including the symbols as those of the first embodiment is used in the description of the configuration and basic operation of the compressor in the second embodiment, and contents of the compression stroke which are different from those of the first embodiment will mainly be described here. In the compression stroke, piston 16 starts in a direction of an arrow y from a state immediately before the compressing operation is started shown in FIG. 12A, and when a pressure in compression chamber 13 becomes higher than that in suction muffler 54 and suction valve 20 closes, compression chamber 13 is closed as shown in FIG. 12B. When piston 16 operates in the direction of the top dead center, i.e., in a direction where the capacity decreases, working fluid 3 is compressed.

At this time, near top end surface 24 of piston 16, working fluid 3 in compression chamber 13 flows from an inner peripheral surface of compression chamber 13 toward discharge hole 19 along the inclined bottom surface of recess 25 a as shown with an arrow Y by recess 25 a formed in top end surface 24 of piston 16.

Since the bottom surface of recess 25 a is inclined, it can be estimated that the flow is more positive as compared with the first embodiment.

When a pressure in compression chamber 13 becomes higher than that in head space 56 and discharge valve 21 opens as shown in FIG. 12C, working fluid 3 near discharge hole 19 swiftly flows toward discharge hole 19 as shown with an arrow Y1, working fluid 3 passes through discharge hole 19 and is discharged into head space 56.

Working fluid 3 in region Z (near the inner peripheral surface of compression chamber 13) which is separated away from discharge hole 19 and which is shown in FIG. 10 receives influence of flow shown with the arrow Y1 as shown with an arrow Y2 in FIG. 12C, a portion of working fluid 3 flows toward the inner peripheral surface of compression chamber 13, and it is normally estimated that discharging speed from discharge hole 19 becomes slow.

According to a configuration of the second embodiment, however, since recess 25 a is provided in top end surface 24 of piston 16, it is estimated that working fluid 3 staying near the inner peripheral surface of compression chamber 13 flows constantly by recess 25 a, and working fluid 3 is guided toward projection 26.

As a result, like the first embodiment, when a path leading to discharge hole 19 becomes narrow since piston 16 reaches a position near the top dead center, it is estimated that working fluid 3 remaining in region Z is induced by a flow of working fluid 3 which flows through recess 25 a of top end surface 24 of piston 16 and which is shown with an arrow Y3, and working fluid 3 is smoothly discharged from discharge hole 19.

Further, since the bottom surface of recess 25 a is inclined toward projection 26 of top end surface 24 facing discharge hole 19, it is estimated that a flow formed by recess 25 a becomes more positive as compared with the first embodiment.

Therefore, it can be expected that a discharge amount of working fluid 3 which remains in region Z near the inner peripheral surface of compression chamber 13 increases, the remaining weight is reduced, the amount of re-expansion is suppressed and the volumetric efficiency can further be enhanced.

As the remaining working fluid 3 is reduced, it is possible to further moderate the local pressure rise mainly around outer peripheral edge 27 of top end surface 24 of piston 16 generated by residence of working fluid 3 in region Z of piston 16, it is possible to suppress the excessive compression in which the pressure rises more than necessary, to reduce the compressor input, and to enhance the compressor efficiency.

As described above, working fluid 3 staying near the inner peripheral surface of compression chamber 13 is induced by a flow of working fluid 3 flowing through recess 25 a provided in top end surface 24 of piston 16 and is discharged from discharge hole 19. Therefore, the clearance between piston 16 and valve plate 17 can further be narrowed, and the capacity of compression chamber 13 at the position of the top dead center of piston 16 can be set smaller. With this, it can be expected that the weight of remaining working fluid 3 is further reduced, the amount of re-expansion is suppressed and the volumetric efficiency can further be enhanced.

Further, since projection 26 which enters discharge hole 19 is formed on top end surface 24 of piston 16, projection 26 enters discharge hole 19 in the discharge stroke, the capacity of compression chamber 13 also including the capacity of discharge hole 19 in the top dead center position of piston 16 can be reduced, the weight of remaining working fluid is reduced and with this, the amount of re-expansion can be reduced and the volumetric efficiency can further be enhanced.

In the second embodiment, discharge hole 19 is provided at a position which is offset from a central portion of top end surface 24 with respect to top end surface 24 of piston 16. Hence, recess 25 a provided in top end surface 24 of piston 16 is oriented to projection 26 of top end surface 24 of piston 16 facing discharge hole 19 from outer peripheral edge 27 of piston 16 farthest from discharge hole 19.

Also if discharge hole 19 reaches the central portion of top end surface 24 of piston 16, a similar effect can be expected by providing recess 25 a such as to extend from outer peripheral edge 27 of the piston where working fluid 3 stays toward the position facing discharge hole 19.

Although projection 26 is formed into the truncated conical shape in the second embodiment, the shape of projection 26 is not limited to the truncated conical shape, and even if projection 26 is formed into a truncated polygonal pyramid shape such as a truncated square pyramid shape, a similar effect can be expected.

Although projection 26 is provided on top end surface 24 of piston 16 in the second embodiment, even if top end surface 24 is not provided with projection 26, it is possible to induce working fluid 3 remaining in region Z of piston 16 shown in FIG. 10 and to guide working fluid 3 into discharge hole 19 by a forcible flow of working fluid 3 flowing through recess 25 a.

Therefore, also in the piston configuration in which top end surface 24 of piston 16 is not provided with projection 26, it is possible to expect the effect of reducing the weight of working fluid 3 remaining in compression chamber 13, suppressing the amount of re-expansion, and enhancing the volumetric efficiency.

Third Embodiment

FIG. 13 is a perspective view of a piston of a reciprocating compressor according to a third embodiment of the invention. FIG. 14 is a plan view of the piston of the reciprocating compressor according to the third embodiment of the invention. FIG. 15 is a sectional view of the reciprocating compressor according to the third embodiment of the invention taken along the 15-15 line in FIG. 13. The same or corresponding constituent elements as those of the first embodiment are designated with the same symbols and the third embodiment is described.

As shown in FIGS. 13, 14 and 15, piston 16 of the reciprocating compressor according to the third embodiment of the invention is different from the configuration of piston 16 of the second embodiment in that a plurality of recesses 25 a, 25 b and 25 c are disposed on top end surface 24 of piston 16 in a fan-shape extending around an opposite position of top end surface 24 facing discharge hole 19. Like the first embodiment, projection 26 is provided at the opposite position of top end surface 24 of piston 16 facing discharge hole 19.

The plurality of recesses 25 a, 25 b and 25 c correspond to induction means of the invention and like recess 25 of the second embodiment, a bottom surface of each of recesses 25 a, 25 b and 25 c is formed into inclined in a manner to increase a distance from valve plate 17 toward the opposite position of top end surface 24 facing discharge hole 19.

Next, operation of the reciprocating compressor including piston 16 having the above-described configuration is described.

Piston 16 having the above-described configuration is used instead of piston 16 of the compressor described in the first embodiment, the same description including the symbols as those of the first embodiment is used in the description of the configuration and basic operation of the compressor in the third embodiment, and contents of the compression which are different from those of the first embodiment will mainly be described here.

In the above configuration, in the case of the third embodiment, since working fluid 3 staying in region Z shown in FIG. 14 is guided to discharge hole 19 by the plurality of recesses 25 a, 25 b and 25 c from the compression stroke to the discharge stroke, guiding effect from a wide range can be expected as compared with guiding effect exerted by one recess 25 or 25 a shown in first, second embodiment, it is possible to suppress the disturbance of a flow of working fluid 3 staying in region Z shown in FIGS. 4 and 10 described in the first and second embodiments toward discharge hole 19 at the time of the discharge stroke.

As a result, the weight of working fluid 3 remaining in region Z shown in FIG. 14 can be reduced and due to this, it is possible to reduce, to a minimum, the capacity of the very small space of compression chamber 13 at the top dead center position of piston 16. With this, the weight of remaining working fluid 103 can further be reduced.

Therefore, the amount of re-expansion of remaining working fluid 3 is suppressed and with this, it is possible to increase a suction amount of working fluid 3 in the suction stroke, and the volumetric efficiency can be enhanced.

It is possible to moderate the local pressure rise caused by residence of working fluid 3 staying near the inner peripheral surface of compression chamber 13, to reduce the compressor input, and to enhance the compressor efficiency.

Even if a plurality of recesses 25 of the first embodiment is provided and they are disposed in the fan-shape like the third embodiment, a similar effect can be expected.

Fourth Embodiment

FIG. 16 is a perspective view of a piston of a reciprocating compressor according to a fourth embodiment of the invention. FIG. 17 is a plan view of the piston of the reciprocating compressor according to the fourth embodiment. FIG. 18 is a sectional view of the reciprocating compressor according to the fourth embodiment taken along the 18-18 line in FIG. 16. The same or corresponding constituent elements as those of the first embodiment are designated with the same symbols and the third embodiment is described.

As shown in FIGS. 16, 17 and 18, piston 16 of the reciprocating compressor in the fourth embodiment of the invention is different from those of the first, second and third embodiments in a configuration of top end surface 24 of piston 16.

That is, piston 16 is different from those of the previous embodiments in that flat inclined surface 24 a is provided on top end surface 24 of piston 16, inclined surface 24 a is separated away from valve plate 17 toward an opposite position of top end surface 24 facing discharge hole 19 from outer peripheral edge 27 of piston 16 farthest from the opposite position. Projection 26 corresponds to induction means of the invention, and projection 26 is provided at the position of top end surface 24 facing discharge hole 19 like the first, second and third embodiments.

Next, operation of the reciprocating compressor including piston 16 having the above-described configuration is described.

Piston 16 having the above-described configuration is used instead of piston 16 of the compressor described in the first embodiment, the same description including the symbols as those of the first embodiment is used in the description of the configuration and basic operation of the compressor in the fourth embodiment, and contents of the compression which are different from those of the first embodiment will mainly be described here.

In the configuration, in the case of the fourth embodiment, working fluid 3 staying in region Z is guided to discharge hole 19 by flat inclined surface 24 a from the compression stroke to the discharge stroke. Therefore, guiding effect from a wider range can be expected as compared with the guiding effect obtained by the recesses 25, 25 a, 25 b and 25 c which partially form the specific flow shown in the previous first, second and third embodiments, it is possible to more smoothly discharge working fluid 3 staying in region Z shown in FIGS. 4, 10 and 14 described in the first, second and third embodiments during the discharge stroke, and effect of further reducing the remaining amount can be expected.

Therefore, like the first, second and third embodiments, it is possible to expect that the weight of working fluid 3 can be reduced, the volumetric efficiency can be enhanced, the compressor input can be reduced, and the compressor efficiency can be enhanced.

According to the invention, there is provided a reciprocating compressor comprising an electromotive element and a compressing element driven by the electromotive element housed in a container, the compressing element including a cylinder block constituting a compression chamber, a piston movable in reciprocating motion in the compression chamber, and a valve plate disposed to close an open end of the compression chamber and having a discharge hole communicating between inside and outside of the compression chamber are in communication with each other, induction means is provided on a top end surface confronting the valve plate for guiding working fluid staying near an inner peripheral surface of the compression chamber from an outer peripheral edge of the top end surface toward an opposite position of the top end surface facing the discharge hole.

According to this configuration, at the time of the compression stroke in which the piston moves from the bottom dead center to the top dead center, working fluid staying near the inner peripheral surface of the compression chamber separated away from the discharge hole (outer peripheral edge of the piston top end surface) can be guided to a position of the top end surface facing the discharge hole by the induction means.

As a result, it is possible to reduce the weight of working fluid remaining in the clearance capacity between the piston and the valve plate, to suppress the amount of re-expansion of the remaining working fluid at the time of the suction stroke, and to enhance the volumetric efficiency. It is possible to suppress the excessive compression which may occur when working fluid stays near the compression chamber, to reduce the compressor input and to enhance the compressor efficiency.

In the invention, the induction means is a recess of a predetermined width extending from an outer peripheral edge of the piston toward the opposite position of the top end surface facing the discharge hole.

According to this configuration, at the time of the compression stroke in which the piston moves from the bottom dead center to the top dead center, working fluid staying near the inner peripheral surface of the compression chamber separated away from the discharge hole (outer peripheral edge of the piston top end surface) can be guided to the opposite position of the top end surface facing the discharge hole along the recess.

As a result, it is possible to suppress the amount of re-expansion of remaining working fluid in the suction stroke, and to enhance the volumetric efficiency. It is possible to suppress the excessive compression which may occur when working fluid stays near the compression chamber, to reduce the compressor input and to enhance the compressor efficiency. Further, since the induction means is the recess having the predetermined width, it is easy to form the recess, and the productivity is not extremely lowered.

Further, in the invention, a bottom surface of the recess is inclined in a manner to increase a distance from the valve plate toward the opposite position of the top end surface of the piston facing the discharge hole.

According to this configuration, behavior of working fluid in the compression chamber in the compression stroke produces a flow moving from a shallow side to a deep side in the recess, and working fluid is discharged from the discharge hole. At this time, working fluid especially staying near the inner peripheral surface of the compression chamber is induced by the flow around the recess and is guided to the discharge hole, it is possible to prevent the working fluid from staying near the inner peripheral surface of the compression chamber, and to further enhance the effect obtained by claim 1.

Further, in the invention, the recess is provided along a diametric direction of the top end surface through the opposite position facing the discharge hole, the recess extends from the outer peripheral edge of the top end surface farthest from the discharge hole to the opposite position.

According to this configuration, working fluid staying near the inner peripheral surface of the compression chamber can be guided along the inside of the recess. As a result, it is possible to further prevent working fluid in the top dead center position of the piston from staying, and to enhance the compressor efficiency.

Further, in the invention, the reciprocating compressor further comprising a plurality of recesses formed radially around the opposite position of the top end surface facing the discharge hole.

According to this configuration, since working fluid staying near the inner peripheral surface of the compression chamber can be guided toward the discharge hole by the plurality of recesses, it is possible to suppress the disturbance of the flow of working fluid guided to the discharge hole. As a result, a further remaining-suppressing effect of working fluid at the top dead center position of the piston can be expected, and it is possible to expect that the compressor efficiency is further enhanced.

Further, in the invention, the induction means is a flat inclined surface formed in a manner to increase a distance from the valve plate as the surface extends from the outer peripheral edge of the piston farthest from the opposite position of the top end surface facing the discharge hole toward the opposite position.

According to this configuration, at the time of the compression stroke in which the piston moves from the bottom dead center to the top dead center, as the piston moves, the capacity of the compression chamber is reduced, working fluid in the compression chamber is compressed and working fluid is discharged from the discharge hole.

At this time, since the top end surface of the piston is inclined, working fluid in the compression chamber flows toward the discharge hole from the outer periphery of the piston which is separated away from the discharge hole. As a result, it is possible to prevent the working fluid in the compression chamber from remaining near the inner peripheral surface when working fluid is discharged from the discharge hole.

Further, in the invention, the reciprocating compressor further comprising a projection provided at the opposite position of the top end surface of the piston facing the discharge hole, wherein the projection enters the discharge hole in the valve plate when the piston reaches a top dead center.

According to this configuration, it is possible to reduce a remaining space capacity of working fluid in a state where the piston reaches the top dead center position including the capacity of the discharge hole.

As a result, it is possible to further reduce the weight of the remaining working fluid, to reduce the amount of re-expansion, and to further enhance the volumetric efficiency of the compressor.

As described above, according to the reciprocating compressor of the present invention, since it is possible to enhance the volumetric efficiency and to enhance the compressor efficiency, the reciprocating compressor can widely be applied not only to a domestic electric refrigerator, but also to other refrigeration apparatus such as an air conditioner and an automatic dispenser, and to an industrial compressor such as an air compressor. 

1. A reciprocating compressor comprising an electromotive element and a compressing element driven by the electromotive element housed in a container, the compressing element including a cylinder block constituting a compression chamber, a piston movable in reciprocating motion in the compression chamber, and a valve plate disposed to close an open end of the compression chamber and having a discharge hole communicating between inside and outside of the compression chamber are in communication with each other, induction means is provided on a top end surface confronting the valve plate for guiding working fluid staying near an inner peripheral surface of the compression chamber from an outer peripheral edge of the top end surface toward an opposite position of the top end surface facing the discharge hole.
 2. The reciprocating compressor according to claim 1, wherein the induction means is a recess of a predetermined width extending from the outer peripheral edge of the piston toward the opposite position of the top end surface acing the discharge hole.
 3. The reciprocating compressor according to claim 2, wherein a bottom surface of the recess is inclined in a manner to increase a distance from the valve plate toward the opposite position of the top end surface of the piston facing the discharge hole.
 4. The reciprocating compressor according to claim 2, wherein the recess is provided along a diametric direction of the top end surface through the opposite position facing the discharge hole, the recess extends from the outer peripheral edge of the top end surface farthest from the discharge hole to the opposite position.
 5. The reciprocating compressor according to claim 3, wherein the recess is provided along a diametric direction of the top end surface through the opposite position facing the discharge hole, the recess extends from the outer peripheral edge of the top end surface farthest from the discharge hole to the opposite position.
 6. The reciprocating compressor according to claim 2, further comprising a plurality of recesses formed radially around the opposite position of the top end surface facing the discharge hole.
 7. The reciprocating compressor according to claim 3, further comprising a plurality of recesses formed radially around the opposite position of the top end surface facing to the discharge hole.
 8. The reciprocating compressor according to claim 1, wherein the induction means is a flat inclined surface formed in a manner to increase a distance from the valve plate as the surface extends from the outer peripheral edge of the piston farthest from the opposite position of the top end surface facing the discharge hole toward the opposite position.
 9. The reciprocating compressor according to claim 1, further comprising a projection provided at the opposite position of the top end surface of the piston facing the discharge hole, wherein the projection enters the discharge hole in the valve plate when the piston reaches a top dead center. 